Option 1: Cellulose is a type of complex carbohydrate that provides structural support in plant cells. While it is a product of photosynthesis, it is not the primary product. The primary product refers to the main molecule produced during the process.

Option 2: Glucose is the correct answer. Glucose is a simple sugar that is synthesized by plants through photosynthesis. It serves as the main source of energy for cellular processes in plants. Glucose can be used immediately by the plant for energy, or it can be converted into other storage molecules like starch or transported to other parts of the plant.

Option 3: Glycogen is a storage form of glucose found in animals, not plants. Plants typically store glucose as starch, not glycogen. Therefore, glycogen is not the primary product of photosynthesis.

Option 4: Sucrose is a disaccharide made up of glucose and fructose. While it is a product of photosynthesis, it is not the primary product. Sucrose is often formed in plants after glucose is produced, and it is transported to various parts of the plant for storage or energy.

In conclusion, the primary product of photosynthesis is glucose.